A skylight is a small hole that forms when the roof of a lava tube collapses due to cooling or impact. Skylights can be found in orbital images and provide an entrance to underground caves

The lava can drain away, leaving an empty cave or tube. Sometimes the roof collapses, forming a skylight. The skylight can provide easy access to what could be underground refuges in some cases. 

On Earth, lava tubes are only as large as 14–15 meters (46–49 ft) wide, though they’re typically much narrower. A collapsed ceiling of a Martian lava tube measures 50 meters (150 ft) across, much larger than any Earth lava tubes.

But more commonly, they are found by locating a “skylight” or collapsed lava tube ceiling in an orbital image. That skylight provides an entrance to the underground cave. Lava tubes can be found on Earth, the Moon, and Mars

Lava tubes are most likely to be found in volcanic regions. They can be found on shield and composite volcanoes, where the lava cools near its margins and forms solid lava levées that eventually close over the top of the flow

Lava tubes are the longest and most complicated of volcanic caves. They are the channels of rivers of lava that at some earlier time flowed downslope from a volcanic vent or fissure. Lava tubes develop best in highly fluid lava, notably a basaltic type known as pahoehoe. 

Some examples of lava tubes include: 

• Surtshellir Located in Iceland, this was the longest known lava tube in the world for a long time. 
• Leviathan Cave Located in Kenya, this is the longest lava tube in Africa at 12.5 kilometers. 
• Manjang Cave Located in Jeju Island, South Korea, this cave is more than 8 kilometers long and is a popular tourism spot.

The world’s longest lava tube is Kazumura Cave, located on the Big Island of Hawaii. The cave is 40.7 miles (65.5 km) long and 3,614 feet (1,102 m) deep. It’s part of the 500-year-old ‘Ailā’au lava flow of Kīlauea, the most recently active volcano on the Big Island

Kazumura Cave is a national treasure of both geological and cultural significance. It’s also the longest linear cave in the world, extending further over a straight-line distance more than any other

Yes, Mars has lava tubes. 

Lava tubes are volcanic caverns that form when the surface of lava channels cools and hardens over subsurface lava flows. Mars has many lava tubes, including the largest volcano in the solar system, Olympus Mons

Lava tubes on Mars may be about ten times the volume of those on Earth. Collapsed lava tubes on Mars are about 80 times larger than those on Earth, with diameters of 130 to 1,300 feet (40 to 400 m). 

Most lava tubes on the Moon and Mars likely date back 3–4 billion years, when both bodies were frequently volcanically active

According to Live Science, Martian lava tubes can be 80 times larger than those on Earth, with diameters ranging from 130 to 1,300 feet (40 to 400 m). 

According to Astronomy.com, the larger dimensions of Martian and Lunar lava tubes are due to the lower gravity and its impact on volcanism. 

According to Medium, a skylight near the Martian volcano Pavonis Mons is estimated to have a diameter of 160–190 meters and a depth of at least 115 meters. 

According to NASA, a pit that is about 150 feet (50 meters) across is likely to have an underground tube that is at least this big

Yes, lava can form channels on Mars

Lava can flow and create features that look like stream channels. For example, a 2010 study found that a channel in an ancient Martian “riverbed” was actually built by lava flows, not liquid water. 

Lava channels are streams of fluid lava contained within zones of static lava or lava levees. The initial channel may not contain levees, but the parental flow solidifies over what develops into the channel and creates natural levees. 

Scientists identify lava channels to understand the history of a region on Mars

Skylights on Mars are circular features that appear as dark, nearly circular features on the surface of Mars. They are formed by partial cave ceiling collapse, and provide access to subsurface voids

Skylights are different from typical pit craters because they lack sloped walls or visible floors. 

In 2007, the Mars Odyssey Thermal Emission Imaging observed seven possible skylight entrances into Martian caves on and around the flanks of Arsia Mons. 

Martian caves have renewed interest in the field of speleology because they are potential destinations for future human residences

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